Crushing analysis and multi-objective optimization of different length bi-thin walled cylindrical structures under axial impact loading

This article attempts to increase the crashworthiness characteristics of energy absorbers. It is found that the effect of the bi-tubular arrangement on the energy absorption and peak force is nonlinear. This nonlinearity is somewhat related to friction but is mostly related to the changing of buckling modes. Therefore, it is possible to reach higher Specific Absorbed Energy (SAE) in the bi-tubular case than with two tubes since the weight is the same in both arrangements while the energy absorption is higher in the bi-tubular case. To exploit this, multi-objective optimization of bi-thin walled cylindrical aluminium tubes under axial impact loading is performed. The absorbed energy and the SAE are considered as the objective functions while the maximum crush load is regarded as a constraint. Finally, the optimal dimensions of tubes are found in order to maximize the SAE and energy absorption for a specified maximum crushing force.     

Synthesis and characterization of novel aromatic polyamides bearing CF3, quinoxaline‐anthraquinone pendants: Study of photophysical and electrochemical properties by using nanocomposite electrode paste

A new aromatic diamine, 2,3‐bis(4‐(4‐amino‐2‐(trifluoromethyl) phenoxy)phenyl)naphtho[2,3‐f]quinoxaline‐7,12‐dione, was synthesized and fully characterized by using FTIR, ¹H and ¹³C NMR, DEPT technique, and elemental analysis. A series of novel fluorescent anthraquinone‐quinoxaline containing polyamides (PAs) with inherent viscosities of 0.39–0.62 dL/g was prepared by direct polycondensation of the diamine with various dicarboxylic acids. These PAs were readily soluble in many polar aprotic organic solvents and could be solution‐cast into tough and flexible films. The PAs exhibited glass transition temperatures (T_g)s between 230 and 323°C, and 10% weight loss temperatures in the range of 362–433°C in N₂. All of the PAs have fluorescence emission in solution and in solid state with maxima around 452–510 nm and with the quantum yields in the range of 6–17%. Also, cyclic voltammetry (CV) method was used to study the electrochemical oxidation behavior of these polymers at the surface of a modified multiwalled carbon nanotube (MWCNT)s glassy electrode. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Bird strike analysis on a typical helicopter windshield with different lay-ups

In the current paper, bird strike to a typical helicopter windshield is investigated using smoothed particles hydrodynamic (SPH) finite element method. Five types of lay-ups in a windshield (single layer stretch acrylic, single layer glass, two-wall cast acrylic, acrylic with Polyvinyl butyral (PVB) interlayer and glass with PVB interlayer) is considered and in each case the thickness which prevents the bird from perforating the windshield is calculated. Since helicopters can have lateral movement in addition to their longitudinal movement, the effect of incident angle on the integrity of windshield is also investigated. Simulations showed that among the five cases presented, glass with PVB interlayer can be the best choice for being used in windshield against bird strike. Another conclusion is that for the same initial velocity, the angled impact can cause more damage in the windshield than the direct impact.     

Analytical solution for static and dynamic analysis of FGP cylinders integrated with FG-GPLs patches exposed to longitudinal magnetic field

Motivated by progressive sandwich structures’ usage due to their high strength to weight ratio in different industries, the current paper aimed at evaluating static and dynamic behaviors of three-layered cylinders including FG porous core and two graphene nanoplatelet (GPLs)-reinforced composite as face sheets. The whole sandwich cylinder rests on Pasternak substrate and it is also exposed to a longitudinal magnetic field. Epoxy has used as matrix and GPLs as the reinforcing phases for top and bottom face sheets and based on the rule of mixture and Halpin–Tsai micromechanical models, effective values for mechanical properties of skins are gained. Besides, regarding the integrity of current research, all layers of model are assumed to be FG, which means for the porous core the placement of the pores is considered and for the faces, the GPLs dispersion patterns are regarded. Among different shell theories, sinusoidal shear deformation shells theory (SSDST) is utilized to define displacement components along with the major axes. Hamilton’s principle is hired to attain governing equations for vibrational and buckling analyses. In the end, the effects of different variables’ alternation as the model’s geometry, foundation moduli, mode number, and mid-radius on vibrational and buckling behaviors are interpreted in type of different plots and tables. Pores’ placement and GPLs dispersion patterns play important roles in static and dynamic responses of the under-consideration cylinder. The outcomes of this study may help to create more efficient engineering structures such as pressure vessels.